8-Speed Transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets having six torque-transmitting mechanisms and two fixed interconnections. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting mechanisms provide interconnections between various gear members, the transmission housing and with the input member, and are operated in combinations of three to establish eight forward speed ratios and one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having threeplanetary gear sets that are controlled by six torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission having three planetary gear sets controlled to provideeight forward speed ratios and one reverse speed ratio.

The transmission family of the present invention has three planetarygear sets, each of which includes a first, second and third member,which members may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawing (i.e., left to right, right to left,etc.). Additionally, the first, second or third members of each gear setmay be counted “first” to “third” in any order in the drawing (i.e., topto bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the third member ofthe first planetary gear set with the third member of the secondplanetary gear set.

A second interconnecting member continuously connects the second memberof the second planetary gear set with the first member of the thirdplanetary gear set.

A first torque transmitting device, such a brake, selectively connectsthe first member of the first planetary gear set with a stationarymember (transmission housing/casing).

A second torque transmitting device, such as a brake, selectivelyconnects the third member of the second planetary gear set with astationary member (transmission housing/casing).

A third torque transmitting device, such as a brake, selectivelyconnects the second member of the second planetary gear set with astationary member (transmission housing/casing).

A fourth torque transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with thesecond member of the second planetary gear set.

A fifth torque transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with thesecond member of the third planetary gear set.

A sixth torque transmitting device, such as a clutch, selectivelyconnects the first member of the second planetary gear set with thesecond member of the third planetary gear set.

The six torque-transmitting mechanisms are selectively engageable incombinations of three to yield eight forward speed ratios and onereverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention; and

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes three planetary gear sets20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the ring gear member 34 and the sun gear member 32.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear arrangement also includes six torque-transmittingmechanisms 50, 52, 54, 55, 56 and 57. The torque-transmitting mechanisms50, 52 and 54 are a stationary-type torque-transmitting mechanism,commonly termed brakes or reaction clutches. The torque-transmittingmechanisms 55, 56 and 57 are rotating-type torque-transmittingmechanisms, commonly termed clutches.

The input member 17 is continuously connected with the sun gear member32 of the planetary gear set 30. The output member 19 is continuouslyconnected with the ring gear member 44 of the planetary gear set 40. Thefirst interconnecting member 70 continuously connects the ring gearmember 24 of the planetary gear set 20 with the ring gear member 34 ofthe planetary gear set 30. The second interconnecting member 72continuously connects the planet carrier assembly member 36 of theplanetary gear set 30 with the sun gear member 42 of the planetary gearset 40.

A first torque transmitting device, such as brake 50, selectivelyconnects the sun gear member 22 of the planetary gear set 20 with thetransmission housing 60. A second torque transmitting device, such asbrake 52, selectively connects the ring gear member 34 of the planetarygear set 30 with the transmission housing 60. A third torquetransmitting device, such as brake 54, selectively connects the planetcarrier assembly member 36 of the planetary gear set 30 with thetransmission housing 60. A fourth torque transmitting device, such asclutch 55, selectively connects the planet carrier assembly member 26 ofthe planetary gear set 20 with the planet carrier assembly member 36 ofthe planetary gear set 30. A fifth torque transmitting device, such asclutch 56, selectively connects the planet carrier assembly member 26 ofthe planetary gear set 20 with the planet carrier assembly member 46 ofthe planetary gear set 40. A sixth torque transmitting device, such asclutch 57, selectively connects the sun gear member 32 of the planetarygear set 30 with the planet carrier assembly member 46 of the planetarygear set 40.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting mechanisms are selectively engaged incombinations of three to provide eight forward speed ratios and onereverse speed ratio all with single transition shifts with a doubleoverdrive.

The reverse speed ratio is established with the engagement of the brake52 and clutches 55, 56. The brake 52 engages the ring gear member 34 andthe ring gear member 24 via interconnecting member 70 with thetransmission housing 60. The clutch 55 engages the planet carrierassembly member 26 with the planet carrier assembly member 36 and thesun gear member 42 via interconnecting member 72. The clutch 56 engagesthe planet carrier assembly member 26 with the planet carrier assemblymember 46. The sun gear member 32 rotates at the same speed as the inputmember 17. The ring gear member 34 and ring gear member 24 do notrotate. The planet carrier assembly member 36, planet carrier assemblymember 26, planetary gear set 40 and output member 19 rotate at the samespeed. The speed of the planet carrier assembly member 36, and thereforethe output member 19, is determined from the speed of the sun gearmember 32 and the ring gear/sun gear tooth ratio of the planetary gearset 30. The numerical value of the reverse speed ratio is determinedutilizing the ring gear/sun gear tooth ratios of the planetary gear set30.

The first forward speed ratio is established with the engagement of thebrakes 50, 52 and the clutch 56. The brake 50 engages the sun gearmember 22 with the transmission housing 60. The brake 52 engages thering gear member 34 and the ring gear member 24 via interconnectingmember 70 with the transmission housing 60. The clutch 56 engages theplanet carrier assembly member 26 with the planet carrier assemblymember 46. The sun gear member 32 rotates at the same speed as the inputmember 17. The ring gear member 34, planetary gear set 20 and planetcarrier assembly member 46 do not rotate. The planet carrier assemblymember 36 and sun gear member 42 rotate at the same speed. The speed ofthe planet carrier assembly member 36 is determined from the speed ofthe sun gear member 32 and the ring gear/sun gear tooth ratio of theplanetary gear set 30. The ring gear member 44 and output member 19rotate at the same speed. The speed of the ring gear member 44, andtherefore the output member 19, is determined from the speed of the sungear member 42 and the ring gear/sun gear tooth ratio of the planetarygear set 40. The numerical value of the first forward speed ratio isdetermined utilizing the ring gear/sun gear tooth ratios of theplanetary gear sets 30 and 40.

The second forward speed ratio is established with the engagement of thebrakes 50, 54 and clutch 56. The brake 50 engages the sun gear member 22with the transmission housing 60. The brake 54 engages the planetcarrier assembly member 36 and the sun gear member 42 viainterconnecting member 72 with the transmission housing 60. The clutch56 engages the planet carrier assembly member 26 with the planet carrierassembly member 46. The sun gear member 32 rotates at the same speed asthe input member 17. The planet carrier assembly member 36 and sun gearmember 42 do not rotate. The ring gear member 34 and ring gear member 24rotate at the same speed. The speed of the ring gear member 34 isdetermined from the speed of the sun gear member 32 and the ringgear/sun gear tooth ratio of the planetary gear set 30. The sun gearmember 22 does not rotate. The planet carrier assembly member 26 andplanet carrier assembly member 46 rotate at the same speed. The speed ofthe planet carrier assembly member 26 is determined from the speed ofthe ring gear member 24 and the ring gear/sun gear tooth ratio of theplanetary gear set 20. The ring gear member 44 and output member 19rotate at the same speed. The speed of the ring gear member 44, andtherefore the output member 19, is determined from the speed of theplanet carrier assembly member 46 and the ring gear/sun gear tooth ratioof the planetary gear set 40. The numerical value of the second forwardspeed ratio is determined utilizing the ring gear/sun gear tooth ratiosof the planetary gear sets 20, 30 and 40.

The third forward speed ratio is established with the engagement of thebrake 50 and the clutches 55, 56. The brake 50 engages the sun gearmember 22 with the transmission housing 60. The clutch 55 engages theplanet carrier assembly member 26 with the planet carrier assemblymember 36 and the sun gear member 42 via interconnecting member 72. Theclutch 56 engages the planet carrier assembly member 26 with the planetcarrier assembly member 46. The sun gear member 32 rotates at the samespeed as the input member 17. The ring gear member 34 and ring gearmember 24 rotate at the same speed. The planet carrier assembly member36, planet carrier assembly member 26, planetary gear set 40 and outputmember 19 rotate at the same speed. The speed of the ring gear member 34is determined from the speed of the sun gear member 32, the speed of theplanet carrier assembly member 36 and the ring gear/sun gear tooth ratioof the planetary gear set 30. The speed of the planet carrier assemblymember 26, and therefore the output member 19, is determined from thespeed of the ring gear member 24 and the ring gear/sun gear tooth ratioof the planetary gear set 20. The numerical value of the third forwardspeed ratio is determined utilizing the ring gear/sun gear tooth ratiosof the planetary gear sets 20 and 30.

The fourth forward speed ratio is established with the engagement of thebrake 50 and the clutches 56, 57. The brake 50 engages the sun gearmember 22 with the transmission housing 60. The clutch 56 engages theplanet carrier assembly member 26 with the planet carrier member 46. Theclutch 57 engages the sun gear member 32 with the planet carrierassembly member 46. The sun gear member 32, planet carrier assemblymember 46 and planet carrier assembly member 26 via interconnectingmember 72 rotate at the same speed as the input member 17. The planetcarrier assembly member 36 and sun gear member 42 rotate at the samespeed. The ring gear member 34 and ring gear member 24 rotate at thesame speed. The speed of the ring gear member 34 is determined from thespeed of the sun gear member 32, the speed of the planet carrierassembly member 36 and the ring gear/sun gear tooth ratio of theplanetary gear set 30. The sun gear member 22 does not rotate. The speedof the planet carrier assembly member 26 is determined from the speed ofthe ring gear member 24 and the ring gear/sun gear tooth ratio of theplanetary gear set 20. The ring gear member 44 and the output member 19rotate at the same speed. The speed of the ring gear member 44, andtherefore the output member 19, is determined from the speed of the sungear member 42, the speed of the planet carrier assembly member 46 andthe ring gear/sun gear tooth ratio of the planetary gear set 40. Thenumerical value of the fourth forward speed ratio is determinedutilizing the ring gear/sun gear tooth ratios of the planetary gear sets20, 30 and 40.

The fifth forward speed ratio is established with the engagement of theclutches 55, 56, 57. In this configuration, the input member 17 isdirectly connected with the output member 19. The numerical value of thefifth forward speed ratio is 1.

The sixth forward speed ratio is established with the engagement of thebrake 50 and the clutches 55, 57. The brake 50 engages the sun gearmember 22 with the transmission housing 60. The clutch 55 engages theplanet carrier assembly member 26 with the planet carrier assemblymember 36 and with the sun gear member 42 via interconnecting member 72.The clutch 57 engages the sun gear member 32 with the planet carrierassembly member 46. The sun gear member 32 and planet carrier assemblymember 46 rotate at the same speed as the input member 17. The planetcarrier assembly member 26, planet carrier assembly member 36 and sungear member 42 rotate at the same speed. The ring gear member 34 andring gear member 24 rotate at the same speed. The speed of the ring gearmember 34 is determined from the speed of the sun gear member 32, thespeed of the planet carrier assembly member 36 and the ring gear/sungear tooth ratio of the planetary gear set 30. The sun gear member 22does not rotate. The speed of the planet carrier assembly member 26 isdetermined from the speed of the ring gear member 24 and the ringgear/sun gear tooth ratio of the planetary gear set 20. The ring gearmember 44 and output member 19 rotate at the same speed. The speed ofthe ring gear member 44, and therefore the output member 19, isdetermined from the speed of the sun gear member 42, the speed of theplanet carrier assembly member 46 and the ring gear/sun gear tooth ratioof the planetary gear set 40. The numerical value of the sixth forwardspeed ratio is determined utilizing the ring gear/sun gear tooth ratiosof the planetary gear sets 20, 30 and 40.

The seventh forward speed ratio is established with the engagement ofthe brakes 50, 54 and clutch 57. The brake 50 engages the sun gearmember 22 with the transmission housing 60. The brake 54 engages theplanet carrier assembly member 36 and sun gear member 42 viainterconnecting member 72 with the transmission housing 60. The clutch57 engages the sun gear member 32 with the planet carrier assemblymember 46. The sun gear member 32 and planet carrier assembly member 46rotate at the same speed as the input member 17. The planet carrierassembly member 36, sun gear member 42 and sun gear member 22 do notrotate. The ring gear member 34 and ring gear member 24 rotate at thesame speed. The speed of the ring gear member 34 is determined from thespeed of the sun gear member 32 and the ring gear/sun gear tooth ratioof the planetary gear set 30. The ring gear member 44 and output member19 rotate at the same speed. The speed of the ring gear member 44, andtherefore the output member 19, is determined from the speed of theplanet carrier assembly member 46 and the ring gear/sun gear tooth ratioof the planetary gear set 40. The numerical value of the seventh forwardspeed ratio is determined utilizing the ring gear/sun gear tooth ratiosof the planetary gear sets 30 and 40.

The eighth forward speed ratio is established with the engagement of thebrakes 50, 52 and the clutch 57. The brake 50 engages the sun gearmember 22 with the transmission housing 60. The brake 52 engages thering gear member 34 and ring gear member 24 via interconnecting member70 with the transmission housing 60. The clutch 57 engages the sun gearmember 32 with the planet carrier assembly member 46. The sun gearmember 32 and planet carrier assembly member 46 rotate at the same speedas the input member 17. The ring gear member 34 and planetary gear set20 do not rotate. The planet carrier assembly member 36 and sun gearmember 42 rotate at the same speed. The speed of the planet carrierassembly member 36 is determined from the speed of the sun gear member32 and the ring gear/sun gear tooth ratio of the planetary gear set 30.The ring gear member 44 and output member 19 rotate at the same speed.The speed of the ring gear member 44, and therefore the output member19, is determined from the speed of the sun gear member 42, the speed ofthe planet carrier assembly member 46 and the ring gear/sun gear toothratio of the planetary gear set 40. The numerical value of the eighthforward speed ratio is determined utilizing the ring gear/sun gear toothratios of the planetary gear sets 30 and 40.

As set forth above, the engagement schedule for the torque-transmittingmechanisms is shown in the truth table of FIG. 1 b. This truth tablealso provides an example of speed ratios and ratio steps that areavailable in the above described transmission. For example, the stepratio between the first and second forward speed ratios is 1.43, whilethe step ratio between the reverse speed ratio and first forward ratiois −0.59.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members; a first interconnecting member continuouslyconnecting said third member of said first planetary gear set with saidthird member of said second planetary gear set; a second interconnectingmember continuously connecting said second member of said secondplanetary gear set with said first member of said third planetary gearset; a first torque-transmitting mechanism selectively connecting saidfirst member of said first planetary gear set with a stationary member;a second torque-transmitting mechanism selectively connecting said thirdmember of said second planetary gear set with said stationary member; athird torque-transmitting mechanism selectively connecting said secondmember of said second planetary gear set with said stationary member; afourth torque-transmitting mechanism selectively connecting said secondmember of said first planetary gear set with said second member of saidsecond planetary gear set; a fifth torque-transmitting mechanismselectively connecting said second member of said first planetary gearset with said second member of said third planetary gear set; a sixthtorque-transmitting mechanism selectively connecting said first memberof said second planetary gear set with said second member of said thirdplanetary gear set; said torque-transmitting mechanisms being engaged incombinations of three to establish eight forward speed ratios and onereverse speed ratio between said input member and said output member. 2.The transmission defined in claim 1, wherein said first, second andthird torque-transmitting mechanisms comprises brakes, and said fourth,fifth and sixth torque-transmitting mechanisms comprise clutches.
 3. Thetransmission of claim 1, wherein said first, second and third members ofsaid first, second and third planetary gear sets comprise a sun gearmember, a planet carrier assembly member and a ring gear member,respectively.
 4. The transmission of claim 1, wherein said input memberis continuously interconnected with said first member of said secondplanetary gear set, and said output member is continuouslyinterconnected with said third member of said third planetary gear set.5. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having a sungear member, planet carrier assembly member and ring gear member; saidinput member being continuously interconnected with said sun gear memberof said second planetary gear set; said output member being continuouslyinterconnected with said ring gear member of said third planetary gearset; a first interconnecting member continuously connecting said ringgear member of said first planetary gear set with said ring gear memberof said second planetary gear set; a second interconnecting membercontinuously connecting said planet carrier assembly member of saidsecond planetary gear set with said sun gear member of said thirdplanetary gear set; a first torque-transmitting mechanism selectivelyconnecting said sun gear member of said first planetary gear set with astationary member; a second torque-transmitting mechanism selectivelyconnecting said ring gear member of said second planetary gear set withsaid stationary member; a third torque-transmitting mechanismselectively connecting said planet carrier assembly member of saidsecond planetary gear set with stationary member; a fourthtorque-transmitting mechanism selectively connecting said planet carrierassembly member of said first planetary gear set with said planetcarrier assembly member of said second planetary gear set; a fifthtorque-transmitting mechanism selectively connecting said planet carrierassembly member of said first planetary gear set with said planetcarrier assembly member of said third planetary gear set; and a sixthtorque-transmitting mechanism selectively connecting said sun gearmember of said second planetary gear set with said planet carrierassembly member of said third planetary gear set; saidtorque-transmitting mechanisms being engaged in combinations of three toestablish eight forward speed ratios and one reverse speed ratio betweensaid input member and said output member.